1. Field of the Invention
The present invention is generally related to stabilization of soil and other granular materials, and more particularly to containment of and prevention of leaching of hazardous materials from such granular materials.
2. Description of the Related Art
Many techniques have been proposed or tried for eliminating or at least containing hazardous waste materials, such as heavy metals, organic compounds and other toxic or hazardous materials. from contaminated soil and from other granular material. When such toxic or hazardous materials migrate into the soil they are even more difficult and expensive to eliminate or contain. For example, wastes generated at countless mineral mining operations have historically been discharged to the local environment and are only now, as a part of the Super Fund operation, being assessed for the extent and impact of their contamination upon the soil and environment. For example, only now is waste generated at facilities such as the Idaho National Engineering Laboratory, the U.S. Department of Energy's Savannah River, Hanford, Washington sites and Rocky Flats, Colorado nuclear trigger production plant during the cold war being retained and to some extent remediated in temporary storage facilities. Some of these storage facilities have in the past unintentionally or unknowingly produced radioactive and/or heavy metal contamination of the underlying soils. As a result, these soils must be dealt with in a manner to render such contamination benign.
For the most part current efforts to clean up these sites and other historically identified hazardous waste sites around the country and around the world have primarily involved excavation and removal of the contaminated soils to a different location for burial in lined pits, or in remote caves, or in sealed drums. However, such efforts do not eliminate the problem, but only temporarily transfer it to someplace else. More permanent solutions have been primarily directed to high toxicity wastes and volume reduction techniques to make the storage considerations more manageable.
Proposals for stabilization of hazardous materials almost all include some concentration of the soils to reduce their volume. The resultant concentrate can then be stabilized via methods such as mixing with concrete or other binding material, or vitrification via combining the concentrate with silica sand and then heating the mixture at sufficiently high temperature in a furnace to cause vitrification of the mixture. These methods have a relatively high energy cost compared to simple burial or drum containment. However, the long term stability of the vitrified material is more predictable and reliable than burial or containment.
Excavation and transport of contaminated soils to a suitable burial facility or toxic waste concentrating facility for treatment is also very costly and labor intensive. Consequently there remains a need for a cost effective and energy efficient method for stabilizing soils contaminated with hazardous material in a manner such that the soil is rendered effectively harmless without the need for transport or concentration. There is also a need for an energy efficient and cost effective apparatus and method for stabilizing hazardous materials such as low level radioactivity or heavy metal contaminated soils or toxic chemical contaminated mine tailings, preferably in a form that either eliminates leaching of the hazardous material or reduces them to an acceptable level.